Re: Difference between disc method, washer method and shell meth

The disc method for finding a volume of a solid of revolution is what we use if we rotate a single curve around the x- (or y-) axis. If we do that and take slices perpendicular to the axis, we will produce a series of discs (like my watermelon example on this page:)

The integral that you use is not the same as the one used for disks or washers.

I will try to add Shell method to that page sometime soon.

X

Hi Shaikshavali
The disc method for finding a volume of a solid of revolution is what we use if we rotate a single curve around the x- (or y-) axis. If we do that and take slices perpendicular to the axis, we will produce a series of discs (like my watermelon example on this page:)
<a href="/applications-integration/4-volume-solid-revolution.php">4. Volume of Solid of Revolution by Integration</a>
If we rotate an area between 2 curves, and then take slices, we won't have a discs, instead we'll have washers (like the ones given in the pictures at the top of the page above).
The Shell method approaches it from quite a different viewpoint. This time we end up with a set of hollow cylinders (something like a drinking glass). see this page:
<a href="http://tutorial.math.lamar.edu/Classes/CalcI/VolumeWithCylinder.aspx">Pauls Online Notes : Calculus I - Volumes of Solids of Revolution/Method of Cylinder</a>
The integral that you use is not the same as the one used for disks or washers.
I will try to add Shell method to that page sometime soon.